Earth berming means piling earth against the above-ground walls of an ice house, at least 60 cm thick, so the walls sit in ground that stays near the yearly average temperature instead of in summer air. Slope the earth away from the wall so water runs off, keep it dry, and cover it with grass so it does not wash away. Earth is a weaker insulator than sawdust, so berming supports the sawdust layer rather than replacing it.
Part of Ice Houses and Cold Storage
Earth berming banks soil against the outside of a building to use the ground’s steady temperature as part of its insulation.
Ground Temperature Is Steady, And That Is What Berming Borrows
Soil is a slow conductor with a lot of thermal mass. A few metres down its temperature hardly changes through the year and sits close to the average air temperature of the place. Summer air can be much warmer than that. A wall in contact with a thick bank of earth faces the ground’s temperature rather than the air’s. The parent article puts the ground at 10-15 degrees C in most climates. That is a warm figure for ice, so berming helps but does not make the building cold on its own. See Underground and Earth-Sheltered Housing for how ground temperature behaves with depth.
Berming is for the above-ground part of the structure. A pit already surrounded by earth is below-grade (see Below-Grade Design). Where you cannot dig, berming is how you borrow the effect.
What You Need
- Earth — a lot of it. The dug soil from a pit is ideal.
- A drained site — wet soil conducts heat far better than dry soil.
- Grass seed or turf — to stabilise the surface. See Vegetation Cover.
- Tamping tools and a level.
- A wall that can take the load — see the safety note.
Method: Berm The Walls
Step 1: Check the wall. Earth pressing on a wall pushes it inward. A dry-stacked or thin timber wall needs to be thick, braced or tied. If in doubt, build the wall as a retaining wall.
Step 2: Grade the ground. Slope the ground away from the building so water runs off and does not soak into the berm.
Step 3: Place earth in layers. Pile the soil against the wall in layers, tamping each one. The parent article asks for at least 60 cm thickness.
Step 4: Shape the surface. Slope the top and outer face so water sheds. Keep it away from the roof edge so the roof overhang still works. See Roof Design.
Step 5: Seed and protect. Grass roots hold the surface. Without cover, rain washes the bank down.
Step 6: Keep it dry. Drain water away from the toe of the bank. A waterlogged bank turns from insulator to conductor.
Worked Example: The Weight On The Wall
Soil weighs on the order of 1,500-2,000 kg per cubic metre (assumed typical range). A berm 60 cm thick against a wall 1.5 m high has, per metre of wall length, an area of soil in section roughly 0.6 m x 1.5 m = 0.9 m2, so a volume of 0.9 m3 per metre.
- Mass per metre of wall: 0.9 x 1,500 = 1,350 kg to 0.9 x 2,000 = 1,800 kg.
- Weight: 1,350 x 9.81 = 13.2 kN to 1,800 x 9.81 = 17.7 kN per metre of wall length.
Only part of that acts sideways on the wall, but it is the scale of load to expect. A thin or dry-stacked wall must be built for it.
Common Mistakes
- Berming a weak wall — the wall bows in and falls.
- Wet berm — conducts heat instead of resisting it.
- Bare earth — it washes down in the first storm.
- Piling earth against roof timbers — they rot. Keep the earth below the roof edge.
- Expecting the ground to be cold enough alone — at 10-15 degrees C it is not.
Safety
Retained earth is heavy and a poorly built wall fails suddenly
Bermed earth pushes against the wall with a load of the order of tonnes per metre. A wall that gives way can bury anyone nearby. Build the berm up in layers behind an adequate wall, never pile it up against a wall while people are working inside the pit, and keep children and animals away while the bank is new. Tamp in layers so the bank does not slump.
What’s Next
- Learn next: Ice Stacking — load the house
- Combine with: Insulation Methods — the other materials